The invention relates to a device for separating the particle-size spectrum of a polydisperse aerosol, comprising an aerosol channel, a clean gas supply channel, a separation section and at least two discharge channels with a linear flow passage disposed between the aerosol channel and the discharge channels.
Such a separating device is known for example from DE 195 05 341.
Aerosols are used in medicine for inhalation therapy. In the environmental analysis tasks, the devices improve the analysis of atmospheric aerosols. Industrial aerosol processes can be carried out in a more effective manner.
From V. Prodi, C. Melandri, T. DeZaiacomo, G. Tarromi, D. Hochrainer (1979), xe2x80x9cAn Inertial Spectrometer for Aerosol Particlesxe2x80x9d, J. Aerosol Science, 10 (1979) pages 411-419) such an apparatus is known: Inertial Particle Aerosol Classifier (IPAC) . It is possible with the IPAC to filter out of a dry polydisperse aerosol stream a quasi-monodisperse part in the range of 0.8-8 xcexcm with a geometric standard deviation of 1.2-1.3.
The IPAC apparatus is cylindrical in shape and consists of two parts. Into the upper part (separating part) of the apparatus, the polydisperse aerosol flows under pressure between two layers of enveloping air, which is free of particles. Together with the enveloping air, the aerosol is accelerated, through a slot nozzle toward a 90xc2x0 bend. Upon passing the bend, the centrifugal force causes the heavier particles to follow a travel path of greater radius than the smaller particles. The total flow is then divided in the lower part (classification part) into an outer, an intermediate and an inner airflow. With an appropriate adjustment of the different air flows, the intermediate air flow contains a particle fraction with a relatively narrow size distribution.
Furthermore, a virtual impactor is known from Conner, W. D. (1966), xe2x80x9cAn inertial-type particle separator for collecting large samplesxe2x80x9d, J. Air Pollut. Control Assoc. 16 (1966), page 35. This impactor consists of an acceleration nozzle and a collection opening. The aerosol stream is accelerated through the nozzle toward the collection opening in which the classification takes place. A small part of the aerosol volume flow is sucked out through the collection opening, the main flow is sucked out at an angle of 90xc2x0 with respect to the nozzle. In accordance with the different inertias of the various particles, particles, which are larger than the separation size of the impactor, reach the collection opening with the smaller volume flow. The larger volume flow contains all the particles, which are smaller than the separation size of the impactor. The particles in both air flows remain in an airsuspended state. There are several variations of the principle for improvement of the separation efficiency of this virtual impactor. One method is the xe2x80x9cOpposing Jetxe2x80x9d method (K. Willeke and E. Pavlik xe2x80x9cSize classification of fine particles by opposing jetsxe2x80x9d, Environmental Sciences and Technology 12 (1978), pages 563-566), wherein the virtual impactor operates in accordance with a counter-current principle. Other possibilities include the addition of particle-free fresh gas either to the smaller volume flow (H. Masuds, D. Hochrainer, and W. Stober, xe2x80x9cAn improved virtual impactor for particle classification and generation of test aerosols with narrow size distributionsxe2x80x9d, J. Aerosol Sci., 10(1978), pages 275-278) or to the polydispersed aerosol stream (B. T. Chen and H. C. Yeh xe2x80x9cAn improved virtual impactor: design and performancexe2x80x9d, J. Aerosol Sci. 18(1987), pages 203-204).
A disadvantage of the IPAC is that it is suitable only for the classification of a dry aerosol. As a result, no quasi monodisperse fraction can be filtered out of an aqueous polydispersed aerosol using the IPAC as it is possible for example with a nozzle sprayer. The yield of a quasi-monodisperse aerosol in comparison with the polydisperse input aerosol is only 10%.
The main disadvantage of the virtual impactor resides in its relatively indefinite separation capability since a certain amount of particles, which are smaller than the separation size of the impactor, are always contained in the airflow of the large particle. The virtual impactor accordingly provides only for a high enrichment but no separation according to the size of the particles of the polydisperse aerosol. Also, the size range of the aerosol being classified cannot be changed during operation of the impactor in a stepless manner.
Such an apparatus has the disadvantage that it is difficult to adjust and that high turbulences occur in the flow because of the sharp-edged separation surfaces whereby the separation effectiveness is reduced.
It is the object of the present invention to provide a device of the type discussed above which however is so designed that it can be easily assembled and that a quasi-monodisperse fraction can be filtered out of a polydisperse aerosol stream with high efficiency.
In a device for separating the particle size spectrum of a polydisperse aerosol comprising a housing including an inlet part, a guide part, an outlet part, a nozzle insert and a separation insert, all parts are axially symmetrical and joined coaxially by centering fits so that they are easy to manufacture and can be easily assembled and also replaced. The parts are so fitted together that they are automatically centered during assembly while providing for the properly sized aerosol and air supply and particle fraction extraction channels.
A particular advantage of this device, which will be called below IAPS (Inertial Aerosol Particle Separator), resides in the fact that a quasi-monodisperse fraction of an easily steplessly adjustable size range can be derived from an aqueous or a dry polydisperse aerosol flow.
Below, an embodiment of the invention will be described in greater detail on the basis of the accompanying drawings.